Transfer tubes for fluids such as high temperature gases have generally been constructed from nickel or cobalt based alloys. Tubes made from these materials conventionally have a sufficient wall thickness to retain the requisite strength characteristics for rigid tubing so as to withstand service temperatures and pressures. However, in many hot gas transfer applications, rigid transfer tubes are heavy and difficult to manufacture with sufficient wall thickness.
In a common application, energy in the form of heat and pressure is being transferred via a gas. It is recognized that transfer tubes capable of withstanding very high pressures and temperatures will accommodate a higher energy flow in a given amount of time but, unfortunately, unacceptable stresses can be placed on components which mate to rigid transfer tubes when the tubing expands as it is heated to high temperature by the gas being transferred. As a result, there has been an inability to increase efficiency significantly by transferring energy at very high temperatures and pressures.
In a typical example of interest, the energy transfer problem is found in hot gas tubes used to transfer exhaust products from hot gas generators to power gas hydraulic units. The exhaust products created by a hot gas generator are used to spin a turbine which, in turn, rotates an impeller used to pump fluid to provide motive force in a hydraulic system by means of a connecting shaft. Typically, the sizing of the hydraulic system is predicated on the temperature and pressure that can reliably be used to power the turbine.
Unfortunately, the weak link in most existing systems is the transfer tube. It is generally recognized that a transfer tube capable of withstanding greater temperatures and pressures would allow use of a smaller and lighter gas generator. In aerospace applications, where weight and space are at a premium, a savings of this type can be significant.
While overcoming the noted problems, it is also desirable to provide a flexible fluid transfer tube to facilitate installation. It is also desirable to provide a flexible fluid transfer tube that cannot only be used to carry hot gases under pressure, but can also be used to carry any gas or fluid which must be insulated and is typically transferred under pressure. Further, it is desirable to provide a flexible fluid transfer tube capable of either continuous or cyclical use.
Among the efforts to provide a flexible tube is that disclosed in Lockhart U.S. Pat. No. 2,934,095, issued Apr. 26, 1960 in which a flexible metal conduit is formed of a convoluted metal hose having a flexible liner of metal braid. However, Lockhart would not be suitable for preventing a loss of thermal energy from a fluid flowing through the conduit or providing thermal protection for the more highly stressed convoluted metal hose.
An attempt to provide a flexible fluid transfer tube useful over a range of temperatures is disclosed in Aubert et al. U.S. Pat. No. 4,344,462, issued Aug. 17, 1982. Aubert et al. discloses a flexible tubular conduit indicated to be usable from -160.degree. C. to +500.degree. C. by utilizing an insulating material between layers of the conduit. However, once again, there are limitations on the degree to which the Aubert et al. flexible tubular conduit is useful in transferring a fluid requiring insulation.
Among other attempts to provide a flexible fluid transfer tube are those disclosed in U.S. Pat. Nos. 3,086,556; 3,460,579; 3,463,197; 3,725,167; 3,908,703; 4,104,095; 4,106,527; 4,106,528; 4,213,485; and 4,383,554.
The present invention is directed to overcoming the above stated problems and accomplishing the stated objects.